Mr Belford focused on the potential environmental ramifications of such an undertaking.
"Before looking at any water storage scheme the regional council should first demonstrate that it can and will ensure a cleaner, safer river by reducing nutrients and more substantially increasing flows," he said.
Mr Beaven touched on how the project and the information about it had been managed.
"This has been a badly run project: all information and messages have been controlled and managed by a small group within the council and often behind closed doors," he said.
"We four councillors were told so little about what was going on that we started calling ourselves the mushrooms - kept in the dark and fed lots of manure."
Mr Barker, who also chaired the forum, spoke on the latest decision of the regional council: the $43.1 million water-user buy-in.
The crowd didn't hold back on its views. "This dam is a dog, it is a very sick dog and it needs to be mercifully put down," attendee Richard Peach said.
Mr Graham responded by saying it was difficult to stop when there were five councillors against four who relentlessly voted for everything put before them.
"That's fine, that is democracy - but the travesty of that was highlighted at the last meeting," he said.
"No matter how good our debate is, no matter how much we sweat it out, we lose every vote."
One person asked for Mr Scotland's view.
"We are appointed by council and unfortunately, because of the delays that this project has endured for the various reasons, our term has kept on being extended."
"And here we are, still going on this thing still with our brief from council to see that we can get a project that meets their conditions precedent and goes ahead."
Mr Scotland said he was not quite sure what he was meant to do as a director, "other than doing what the shareholders told me I have to do".
"Resign," a voice from the crowd shouted out, followed by a crescendo of voices calling out "Resign, resign."
When approached for comment after the meeting, Mr Pearce said he had no reaction to the call.
"I think the audience gave the councillors some support for the view that these councillors have got," he said.
"That's hardly surprising.
"I would have the view that some things that some councillors said were incorrect, in fact."